To provide an understanding of the importance of the present invention, some discussion of the general class of compounds which might be produced using the invention is in order. The term "detergent" describes such a general class of compounds. Such compounds have the ability to reduce or prevent deposits in engines operated at high temperatures. Additives which disperse sludge formed in engines operated at relatively low temperatures (e.g., those prevailing in short trip, stop-and-go driving conditions) are now termed "dispersants," even though the ultimate result flowing from their use, a "clean" engine, presumes a "detergent" or cleansing action.
The first detergent additives, employed commercially in the late thirties to reduce ring-sticking and ring-groove carbon in diesel engines, were oil-soluble polyvalent metal salts or "soaps" of high molecular weight carboxylic acids. Among the more widely used varieties of salts were aluminum naphthenate, calcium dichlorostearate, calcium phenylstearate, and calcium chlorophenylstearate. Although these additives were effective in improving piston cleanliness and extending the service life of diesel engines between overhauls, they were corrosive to sensitive bearing metals and such corrosion could not be controlled satisfactorily by inhibitors available at the time. They became obsolete when hard but corrosion-susceptible copper-lead bearings began to replace soft but corrosion-resistant Babbitt bearings in the early forties. For a brief period between the obsolescence of carboxylic acid salts and the emergence of detergents which are still used commercially today, oil-soluble polyvalent metals salts (i.e., phenates) of long chain alcohol esters of salicyclic acid found considerable commercial favor. Examples of such salicylate ester salts include magnesium lauryl salicyclate,calcium lauryl salicylate, and calcium octadecyl salicylate. Despite the fact that the prototypes of such detergent additives were first introduced in the 1940 decade, they have retained their commercial importance--in many instances because of improved processing or "chemical modification" techniques which increased their effectiveness substantially.
The following list refers to families of detergent additives believed to be in substantial commercial use:
Sulfonates--The normal and basic metal salts of petroleum sulfonic ("mahogany") and long chain alkyl substituted benzene sulfonic acids.
Phosphonates and/or Thiophosphonates--The normal and basic metal salts of the phosphonic and/or thiophosphonic acids obtained from the reaction of polyolefins such as polyisobutenes with inorganic phosphorus reagents (principally phosphorus pentasulfide).
Phenates--The normal and basic metal salts of alkylphenols, alkylphenol sulfides, and alkylphenol-aldehyde condensation products.
Alkyl Substituted Salicylates--The normal and basic metal salts (carboxylate and carboxylate-phenate salts) of long chain alkyl substituted salicylic acids. These products should not be confused with the obsolete metal phenates of salicyclic acid esters mentioned earlier.
An understanding of the terms "normal salt" and "basic salt" is important with respect to the present invention. A normal salt of an acid is one which contains the stoichiometric amount of metal required for the neutralization of the acidic group or groups present. A basic salt is one which contains more metal than is required for the indicated neutralization reaction. Such excess metal may be present due to a true basic salt structure ##STR1## (postulated structure of basic barium sulfonate containing twice as much barium as the normal sulfonate)
or it may be present in the form of colloidally-dispersed metallic base (hydroxide, oxide, carbonate, etc.).
The excess metal in basic salts is capable of neutralizing acidic contaminants (principally oil oxidation and "blow-by" fuel combustion products) found in used crankcase oils, with the result that corrosive wear of an engine is reduced. Practically all current commercial detergent additives are basic salts. Much has been written on the chemistry of basic detergent additives and their ability to reduce corrosive wear of engines.
Normal metal sulfonates derived from "mahogany" acids (the mahogany-colored petroleum sulfonic acids obtained as a by-product during white oil manufacture) were first employed as detergent additives in commercial crankcase oils during World War II. Almost without exception, the metals present in such sulfonates were calcium or barium. Petroleum sulfonates not only imparted a greater degree of detergency to lubricating oils than carboxylic acid soaps or salicylate ester salts, but were much less corrosive to sensitive bearing metals and responded well to known corrosion inhibitors.
In the period between the close of World War II and 1950, research carried out on petroleum sulfonates indicated that basic products could be prepared by various processing techniques, most of which involve heating the sulfonate with an excess of a metallic base and water at an elevated temperature. These products were found to contain up to twice as much metal as the corresponding normal sulfonates. They soon supplanted normal sulfonates in lubricant formulations because of their superior detergent power and their ability to neutralize acidic contaminants and reduce corrosive wear of engine piston rings and cylinder bores.
The next important development in the continuing research effort to improve the effectiveness of sulfonate detergents occurred in the early fifties, when methods were discovered by which one could prepare fully oilsoluble sulfonates containing from 3 to 10 or 15 times as much metal as the corresponding normal sulfonates. Such highly basic sulfonates, to which coined terms such as "overbased," "superbasic," and "hyperbasic" have been applied in the trade, were found to possess unusually high detergent power and, as might be anticipated, a great capacity to neutralize acidic contaminants.
Hereinafter the term "overbased" will be used. The present invention involves a specific method for making such overbased salts. The manufacture of such overbased sulfonates generally involves a mixing of certain promoters, catalysts, or solvents with a normal sulfonate and a large excess of metallic base, followed by heating and filtration steps. Prior to filtration, carbonation of the reaction mass with carbon dioxide is often used to increase the amount of metal base colloidally dispersed as metal carbonate in the filtered product.
Suitable promoters or catalysts for overbasing processes include phenols (see U.S. Pat. No. 2,616,924); thioacids of phosphorus (see U.S. Pat. No. 2,616,925); alcoholates (see U.S. Pat. No. 2,585,520); alcohols (see U.S. Pat. No. 3,057,896); ketones (see U.S. Pat. No. 3,006,952); and alkanolamines. Metallic bases employed in the preparation of overbased sulfonates are for the most part basic compounds of alkaline earth metals such as calcium, barium, or magnesium.
U.S. Pat. No. 4,261,840 discloses lubricating greases which are formed by overbasing a mixture comprised of a lubricating oil, an alkaline earth metal petroleum sulfonate, and a lower molecular weight sulfonic acid derivative. This patent like the other patents referred to below discusses methods for carrying out overbasing procedures which methods are somewhat more current than the patents referred to above.
U.S. Pat. No. 4,057,504 discloses a method of preparing an overbased lubricating oil additive. The method includes introducing carbon dioxide into a mixture containing an oil-soluble organic acid or metal salt thereof, which acid or salt includes a hydrocarbon having 18 to 150 carbon atoms and an alkaline earth metal compound. The carbon dioxide is introduced at a temperature higher than about 100.degree. C. in a reaction medium of lubricating oil in the presence of a reaction accelerator comprised of a dihydric alcohol, a phenol compound and sulfur. The reaction which takes place completes the carbonation after which all of the volatile components contained in the reaction product are removed.
U.S. Pat. No. 4,051,047 discloses group II metal mixed salts of (A) an oil-soluble hydrocarbyl sulfonic acid; and (B) a polyoxyalkylenated sulfuric acid. Such mixed salts are indicated as being useful rust inhibitors in lubricating oil compositions.
U.S. Pat. No. 4,049,560 discloses a method of producing overbased magnesium phenate detergents. The method includes carbonating a mixture of a sulfur containing phenol, a smaller amount of a sulfonic acid, sulfonate or sulfate, an alcohol, magnesium oxide or hydroxide and a carboxylic acid anhydride or salt thereof. The detergent additives produced by the product are indicated as being useful in connection with lubricating oils.
U.S. Pat. No. 4,615,841 discloses a process for making alkaline-earth metal salts of alkaryl sulfonic acids. The method involves reacting an alkaryl sulfonic acid with alkaline-earth metal oxide in an organic solvent in the presence of 0.05 to less than 2.5 weight percent water.